If I were to ask why doesn't br have a closing tag?
The closing and opening tags are like brackets around the content, the <br/> tag doesn't have any content in it, it can have content before it and content after it, but not in it, so it doesn't act like a bracket.
BR tag doesnt have any content therefore it cannot have any associated opening and closing tags
because its haven't open tag
It doesn't have any content for it. All it does is make the rest of the text on a new line, therefore it does not need a closing tag.